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            <h2 class="toc-title">目录</h2>
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        </div><article class="page single"><h1 class="single-title animated flipInX">Spring源码 - Spring标签解析-BeanDefinitionParser</h1><div class="post-meta">
            <div class="post-meta-line"><span class="post-author"><a href="https://wlizhi.cc" title="Author" target="_blank" rel="noopener noreffer author" class="author"><i class="fas fa-user-circle fa-fw"></i>Wlizhi</a></span>&nbsp;<span class="post-category">收录于 <a href="/categories/spring/"><i class="far fa-folder fa-fw"></i>spring</a></span></div>
            <div class="post-meta-line"><i class="far fa-calendar-alt fa-fw"></i>&nbsp;<time datetime="2020-11-23">2020-11-23</time>&nbsp;<i class="fas fa-pencil-alt fa-fw"></i>&nbsp;约 4319 字&nbsp;
                <i class="far fa-clock fa-fw"></i>&nbsp;预计阅读 9 分钟&nbsp;<span id="/posts/spring/02-spring-tag-parse-bean-definition-parser/" class="leancloud_visitors" data-flag-title="Spring源码 - Spring标签解析-BeanDefinitionParser">
                        <i class="far fa-eye fa-fw"></i>&nbsp;<span class=leancloud-visitors-count></span>&nbsp;次阅读
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                    <span>目录</span>
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  <ul>
    <li><a href="#1-beandefinitionparser接口的定义">1 BeanDefinitionParser接口的定义</a></li>
    <li><a href="#2-componentscanbeandefinitionparser实现流程解析">2 ComponentScanBeanDefinitionParser实现流程解析</a>
      <ul>
        <li><a href="#21-componentscanbeandefinitionparser中的属性">2.1 ComponentScanBeanDefinitionParser中的属性</a></li>
        <li><a href="#22-主流程方法parse">2.2 主流程方法parse()</a></li>
        <li><a href="#23-configurescanner">2.3 configureScanner()</a></li>
        <li><a href="#24-核心方法doscan">2.4 核心方法doScan()</a></li>
        <li><a href="#25-findcandidatecomponents原理解析">2.5 findCandidateComponents原理解析</a></li>
      </ul>
    </li>
    <li><a href="#3-aspectjautoproxybeandefinitionparser">3 AspectJAutoProxyBeanDefinitionParser</a></li>
    <li><a href="#4-annotationconfigbeandefinitionparser">4 AnnotationConfigBeanDefinitionParser</a></li>
    <li><a href="#5-总结">5 总结</a></li>
  </ul>
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            </div><div class="content" id="content"><p>spring源码系列文章，示例代码的中文注释，均是 copy 自 <a href="https://gitee.com/wlizhi/spring-framework" target="_blank" rel="noopener noreffer">https://gitee.com/wlizhi/spring-framework</a> 。</p>
<p>链接中源码是作者从 github 下载，并以自身理解对核心流程及主要节点做了详细的中文注释。</p>
<hr>
<p>本文是对 <a href="/posts/spring/01-spring%e7%a8%8b%e5%ba%8f%e5%85%a5%e5%8f%a3%e5%92%8cxml%e8%a7%a3%e6%9e%90" rel="">Spring程序入口和XML解析</a> 的知识点扩展，详细解析其中提到的BeanDefinitionParser的作用，以及一些典型的XML方式解析的实现类。</p>
<h2 id="1-beandefinitionparser接口的定义">1 BeanDefinitionParser接口的定义</h2>
<hr>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">interface</span> <span class="nc">BeanDefinitionParser</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">	<span class="nd">@Nullable</span>
</span></span><span class="line"><span class="cl">	<span class="n">BeanDefinition</span> <span class="nf">parse</span><span class="o">(</span><span class="n">Element</span> <span class="n">element</span><span class="o">,</span> <span class="n">ParserContext</span> <span class="n">parserContext</span><span class="o">);</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>可以看到，BeanDefinitionParser只有一个方法，负责BeanDefinitaion的解析。参数有节点元素、解析上下文对象。</p>
<p>在Spring中有很多内置的BeanDefinitionParser实现类（<code>之所以说内置，因为它也是可以扩展的</code>），包括XML方式解析、注解方式解析等。
<div class="details admonition note open">
        <div class="details-summary admonition-title">
            <i class="icon fas fa-pencil-alt fa-fw"></i>注意<i class="details-icon fas fa-angle-right fa-fw"></i>
        </div>
        <div class="details-content">
            <div class="admonition-content">ParserContext中封装了BeanDefinitionRegistry对象，用于BeanDefinition的注册。</div>
        </div>
    </div></p>
<p>关于此类的实例从哪里注册、parse方法从哪里调入进来的， <a href="/posts/spring/01-spring%e7%a8%8b%e5%ba%8f%e5%85%a5%e5%8f%a3%e5%92%8cxml%e8%a7%a3%e6%9e%90" rel="">Spring程序入口和XML解析</a> 中有结尾处有详细说明。</p>
<h2 id="2-componentscanbeandefinitionparser实现流程解析">2 ComponentScanBeanDefinitionParser实现流程解析</h2>
<hr>
<h3 id="21-componentscanbeandefinitionparser中的属性">2.1 ComponentScanBeanDefinitionParser中的属性</h3>
<p>ComponentScanBeanDefinitionParser是BeanDefinitionParser的一个实现，用于解析<code>&lt;context:component-scan/&gt;</code>标签的属性。</p>
<p>这个类中定义了一些常量，这些常量是<code>&lt;context:component-scan/&gt;</code>中所有可能用到的属性。比如最常用到的<code>base-package</code>属性。</p>
<p>前面有提到，parse方法的参数中有Element。在解析Element时，会对Element的多个属性进行识别及处理。这些常量的作用就在于此，用来区分Element的不同属性，并做特定的处理。
以下是ComponentScanBeanDefinitionParser中定义的常量：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">ComponentScanBeanDefinitionParser</span> <span class="kd">implements</span> <span class="n">BeanDefinitionParser</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="kd">private</span> <span class="kd">static</span> <span class="kd">final</span> <span class="n">String</span> <span class="n">BASE_PACKAGE_ATTRIBUTE</span> <span class="o">=</span> <span class="s">&#34;base-package&#34;</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="kd">private</span> <span class="kd">static</span> <span class="kd">final</span> <span class="n">String</span> <span class="n">RESOURCE_PATTERN_ATTRIBUTE</span> <span class="o">=</span> <span class="s">&#34;resource-pattern&#34;</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="kd">private</span> <span class="kd">static</span> <span class="kd">final</span> <span class="n">String</span> <span class="n">USE_DEFAULT_FILTERS_ATTRIBUTE</span> <span class="o">=</span> <span class="s">&#34;use-default-filters&#34;</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="kd">private</span> <span class="kd">static</span> <span class="kd">final</span> <span class="n">String</span> <span class="n">ANNOTATION_CONFIG_ATTRIBUTE</span> <span class="o">=</span> <span class="s">&#34;annotation-config&#34;</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="kd">private</span> <span class="kd">static</span> <span class="kd">final</span> <span class="n">String</span> <span class="n">NAME_GENERATOR_ATTRIBUTE</span> <span class="o">=</span> <span class="s">&#34;name-generator&#34;</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="kd">private</span> <span class="kd">static</span> <span class="kd">final</span> <span class="n">String</span> <span class="n">SCOPE_RESOLVER_ATTRIBUTE</span> <span class="o">=</span> <span class="s">&#34;scope-resolver&#34;</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="kd">private</span> <span class="kd">static</span> <span class="kd">final</span> <span class="n">String</span> <span class="n">SCOPED_PROXY_ATTRIBUTE</span> <span class="o">=</span> <span class="s">&#34;scoped-proxy&#34;</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="kd">private</span> <span class="kd">static</span> <span class="kd">final</span> <span class="n">String</span> <span class="n">EXCLUDE_FILTER_ELEMENT</span> <span class="o">=</span> <span class="s">&#34;exclude-filter&#34;</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="kd">private</span> <span class="kd">static</span> <span class="kd">final</span> <span class="n">String</span> <span class="n">INCLUDE_FILTER_ELEMENT</span> <span class="o">=</span> <span class="s">&#34;include-filter&#34;</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="kd">private</span> <span class="kd">static</span> <span class="kd">final</span> <span class="n">String</span> <span class="n">FILTER_TYPE_ATTRIBUTE</span> <span class="o">=</span> <span class="s">&#34;type&#34;</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="kd">private</span> <span class="kd">static</span> <span class="kd">final</span> <span class="n">String</span> <span class="n">FILTER_EXPRESSION_ATTRIBUTE</span> <span class="o">=</span> <span class="s">&#34;expression&#34;</span><span class="o">;</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><h3 id="22-主流程方法parse">2.2 主流程方法parse()</h3>
<p>步骤：</p>
<ol>
<li>获取到标签中<code>base-package</code>属性的值，这个值是必须的。（否则会抛出异常，异常信息<code>At least one base package must be specified</code>）。</li>
<li>创建扫描器：ClassPathBeanDefinitionScanner（mybatis中的扫描器就是继承了它）</li>
<li>调用核心方法doScan（这里解析并注册了BeanDefinition）</li>
<li>注册组件registerComponents（ClassPathBeanDefinitionScanner中，最终是一个空方法，可以不看，BeanDefinition的注册在doScan中做了）</li>
</ol>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">ComponentScanBeanDefinitionParser</span> <span class="kd">implements</span> <span class="n">BeanDefinitionParser</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">    <span class="kd">public</span> <span class="n">BeanDefinition</span> <span class="nf">parse</span><span class="o">(</span><span class="n">Element</span> <span class="n">element</span><span class="o">,</span> <span class="n">ParserContext</span> <span class="n">parserContext</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 获取base-package属性
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="n">String</span> <span class="n">basePackage</span> <span class="o">=</span> <span class="n">element</span><span class="o">.</span><span class="na">getAttribute</span><span class="o">(</span><span class="n">BASE_PACKAGE_ATTRIBUTE</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="n">basePackage</span> <span class="o">=</span> <span class="n">parserContext</span><span class="o">.</span><span class="na">getReaderContext</span><span class="o">().</span><span class="na">getEnvironment</span><span class="o">().</span><span class="na">resolvePlaceholders</span><span class="o">(</span><span class="n">basePackage</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="n">String</span><span class="o">[]</span> <span class="n">basePackages</span> <span class="o">=</span> <span class="n">StringUtils</span><span class="o">.</span><span class="na">tokenizeToStringArray</span><span class="o">(</span><span class="n">basePackage</span><span class="o">,</span>
</span></span><span class="line"><span class="cl">				<span class="n">ConfigurableApplicationContext</span><span class="o">.</span><span class="na">CONFIG_LOCATION_DELIMITERS</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">		<span class="c1">// Actually scan for bean definitions and register them.
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="n">ClassPathBeanDefinitionScanner</span> <span class="n">scanner</span> <span class="o">=</span> <span class="n">configureScanner</span><span class="o">(</span><span class="n">parserContext</span><span class="o">,</span> <span class="n">element</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// TODO 重点：这里执行了具体的解析逻辑。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="n">Set</span><span class="o">&lt;</span><span class="n">BeanDefinitionHolder</span><span class="o">&gt;</span> <span class="n">beanDefinitions</span> <span class="o">=</span> <span class="n">scanner</span><span class="o">.</span><span class="na">doScan</span><span class="o">(</span><span class="n">basePackages</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="n">registerComponents</span><span class="o">(</span><span class="n">parserContext</span><span class="o">.</span><span class="na">getReaderContext</span><span class="o">(),</span> <span class="n">beanDefinitions</span><span class="o">,</span> <span class="n">element</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">		<span class="k">return</span> <span class="kc">null</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p><span id="configureScanner-source"></span></p>
<h3 id="23-configurescanner">2.3 configureScanner()</h3>
<p>从以下源码可以看到，首先设置是否使用默认过滤器，然后创建扫描器ComponentScanBeanDefinitionParser，之后对其他属性进行一些设置。（<code>关注源码中关键点就好，不然会越陷越深</code>）</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">ComponentScanBeanDefinitionParser</span> <span class="kd">implements</span> <span class="n">BeanDefinitionParser</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">    <span class="kd">protected</span> <span class="n">ClassPathBeanDefinitionScanner</span> <span class="nf">configureScanner</span><span class="o">(</span><span class="n">ParserContext</span> <span class="n">parserContext</span><span class="o">,</span> <span class="n">Element</span> <span class="n">element</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 解析配置的属性，use-default-filters如果未定义，默认为true
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="kt">boolean</span> <span class="n">useDefaultFilters</span> <span class="o">=</span> <span class="kc">true</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">		<span class="k">if</span> <span class="o">(</span><span class="n">element</span><span class="o">.</span><span class="na">hasAttribute</span><span class="o">(</span><span class="n">USE_DEFAULT_FILTERS_ATTRIBUTE</span><span class="o">))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="n">useDefaultFilters</span> <span class="o">=</span> <span class="n">Boolean</span><span class="o">.</span><span class="na">valueOf</span><span class="o">(</span><span class="n">element</span><span class="o">.</span><span class="na">getAttribute</span><span class="o">(</span><span class="n">USE_DEFAULT_FILTERS_ATTRIBUTE</span><span class="o">));</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 创建扫描器，其实mybatis中的扫描原理就来自于此，mybatis中的ClassPathMapperScanner继承了ClassPathBeanDefinitionScanner
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="c1">// Delegate bean definition registration to scanner class.
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="n">ClassPathBeanDefinitionScanner</span> <span class="n">scanner</span> <span class="o">=</span> <span class="n">createScanner</span><span class="o">(</span><span class="n">parserContext</span><span class="o">.</span><span class="na">getReaderContext</span><span class="o">(),</span> <span class="n">useDefaultFilters</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 下面的代码是对标签中其他属性的一些设置，其实就是把标签及其属性以java类的描述形式体现。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="n">scanner</span><span class="o">.</span><span class="na">setBeanDefinitionDefaults</span><span class="o">(</span><span class="n">parserContext</span><span class="o">.</span><span class="na">getDelegate</span><span class="o">().</span><span class="na">getBeanDefinitionDefaults</span><span class="o">());</span>
</span></span><span class="line"><span class="cl">		<span class="n">scanner</span><span class="o">.</span><span class="na">setAutowireCandidatePatterns</span><span class="o">(</span><span class="n">parserContext</span><span class="o">.</span><span class="na">getDelegate</span><span class="o">().</span><span class="na">getAutowireCandidatePatterns</span><span class="o">());</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">		<span class="k">if</span> <span class="o">(</span><span class="n">element</span><span class="o">.</span><span class="na">hasAttribute</span><span class="o">(</span><span class="n">RESOURCE_PATTERN_ATTRIBUTE</span><span class="o">))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="n">scanner</span><span class="o">.</span><span class="na">setResourcePattern</span><span class="o">(</span><span class="n">element</span><span class="o">.</span><span class="na">getAttribute</span><span class="o">(</span><span class="n">RESOURCE_PATTERN_ATTRIBUTE</span><span class="o">));</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">		<span class="k">try</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="n">parseBeanNameGenerator</span><span class="o">(</span><span class="n">element</span><span class="o">,</span> <span class="n">scanner</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="k">catch</span> <span class="o">(</span><span class="n">Exception</span> <span class="n">ex</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="n">parserContext</span><span class="o">.</span><span class="na">getReaderContext</span><span class="o">().</span><span class="na">error</span><span class="o">(</span><span class="n">ex</span><span class="o">.</span><span class="na">getMessage</span><span class="o">(),</span> <span class="n">parserContext</span><span class="o">.</span><span class="na">extractSource</span><span class="o">(</span><span class="n">element</span><span class="o">),</span> <span class="n">ex</span><span class="o">.</span><span class="na">getCause</span><span class="o">());</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">		<span class="k">try</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="n">parseScope</span><span class="o">(</span><span class="n">element</span><span class="o">,</span> <span class="n">scanner</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="k">catch</span> <span class="o">(</span><span class="n">Exception</span> <span class="n">ex</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="n">parserContext</span><span class="o">.</span><span class="na">getReaderContext</span><span class="o">().</span><span class="na">error</span><span class="o">(</span><span class="n">ex</span><span class="o">.</span><span class="na">getMessage</span><span class="o">(),</span> <span class="n">parserContext</span><span class="o">.</span><span class="na">extractSource</span><span class="o">(</span><span class="n">element</span><span class="o">),</span> <span class="n">ex</span><span class="o">.</span><span class="na">getCause</span><span class="o">());</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">		<span class="n">parseTypeFilters</span><span class="o">(</span><span class="n">element</span><span class="o">,</span> <span class="n">scanner</span><span class="o">,</span> <span class="n">parserContext</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">		<span class="k">return</span> <span class="n">scanner</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><h3 id="24-核心方法doscan">2.4 核心方法doScan()</h3>
<ol>
<li>扫描出所有满足条件的类，并封装成BeanDefinition</li>
<li>循环扫描到的BeanDefinition集合，依次执行操作。
<ol>
<li>解析@Scope注解</li>
<li>对不同类型的BeanDefinition做不同处理，@Lazy、@DependOn等注解信息封装就是在这里设置的。</li>
<li>校验是否是需要实例化的BeanDefinition，如果为true，则将BeanDefinition包装成BeanDefinitionHolder（这个类里封装了实例名称、别名信息）</li>
</ol>
</li>
</ol>
<p>源码如下：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">ComponentScanBeanDefinitionParser</span> <span class="kd">implements</span> <span class="n">BeanDefinitionParser</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">	<span class="kd">protected</span> <span class="n">Set</span><span class="o">&lt;</span><span class="n">BeanDefinitionHolder</span><span class="o">&gt;</span> <span class="nf">doScan</span><span class="o">(</span><span class="n">String</span><span class="o">...</span> <span class="n">basePackages</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="n">Assert</span><span class="o">.</span><span class="na">notEmpty</span><span class="o">(</span><span class="n">basePackages</span><span class="o">,</span> <span class="s">&#34;At least one base package must be specified&#34;</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 用来装所有扫描到的类的BeanDefinition对象。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="n">Set</span><span class="o">&lt;</span><span class="n">BeanDefinitionHolder</span><span class="o">&gt;</span> <span class="n">beanDefinitions</span> <span class="o">=</span> <span class="k">new</span> <span class="n">LinkedHashSet</span><span class="o">&lt;&gt;();</span>
</span></span><span class="line"><span class="cl">		<span class="k">for</span> <span class="o">(</span><span class="n">String</span> <span class="n">basePackage</span> <span class="o">:</span> <span class="n">basePackages</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="c1">// TODO 重点看：查找候选组件，封装成BeanDefinition。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="n">Set</span><span class="o">&lt;</span><span class="n">BeanDefinition</span><span class="o">&gt;</span> <span class="n">candidates</span> <span class="o">=</span> <span class="n">findCandidateComponents</span><span class="o">(</span><span class="n">basePackage</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">			<span class="k">for</span> <span class="o">(</span><span class="n">BeanDefinition</span> <span class="n">candidate</span> <span class="o">:</span> <span class="n">candidates</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="c1">// 获取到ScopeMetadata，如果类中有@Scope注解，则会将值封装到这个实例中。然后设置到BeanDefinition中。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="n">ScopeMetadata</span> <span class="n">scopeMetadata</span> <span class="o">=</span> <span class="k">this</span><span class="o">.</span><span class="na">scopeMetadataResolver</span><span class="o">.</span><span class="na">resolveScopeMetadata</span><span class="o">(</span><span class="n">candidate</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="n">candidate</span><span class="o">.</span><span class="na">setScope</span><span class="o">(</span><span class="n">scopeMetadata</span><span class="o">.</span><span class="na">getScopeName</span><span class="o">());</span>
</span></span><span class="line"><span class="cl">				<span class="n">String</span> <span class="n">beanName</span> <span class="o">=</span> <span class="k">this</span><span class="o">.</span><span class="na">beanNameGenerator</span><span class="o">.</span><span class="na">generateBeanName</span><span class="o">(</span><span class="n">candidate</span><span class="o">,</span> <span class="k">this</span><span class="o">.</span><span class="na">registry</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="c1">// 对不同类型的BeanDefinition做不同的处理。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="k">if</span> <span class="o">(</span><span class="n">candidate</span> <span class="k">instanceof</span> <span class="n">AbstractBeanDefinition</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">					<span class="n">postProcessBeanDefinition</span><span class="o">((</span><span class="n">AbstractBeanDefinition</span><span class="o">)</span> <span class="n">candidate</span><span class="o">,</span> <span class="n">beanName</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="o">}</span>
</span></span><span class="line"><span class="cl">				<span class="c1">// 对不同类型的BeanDefinition做不同的处理，@Lazy、@DependOn等注解信息封装就是在这里设置的。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="k">if</span> <span class="o">(</span><span class="n">candidate</span> <span class="k">instanceof</span> <span class="n">AnnotatedBeanDefinition</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">					<span class="c1">// 一些注解信息的封装
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>					<span class="n">AnnotationConfigUtils</span><span class="o">.</span><span class="na">processCommonDefinitionAnnotations</span><span class="o">((</span><span class="n">AnnotatedBeanDefinition</span><span class="o">)</span> <span class="n">candidate</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="o">}</span>
</span></span><span class="line"><span class="cl">				<span class="c1">// 校验是否是需要实例化的BeanDefinition，如果为true，则将BeanDefinition包装成BeanDefinitionHolder（这个类里封装了实例名称、别名信息）
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="k">if</span> <span class="o">(</span><span class="n">checkCandidate</span><span class="o">(</span><span class="n">beanName</span><span class="o">,</span> <span class="n">candidate</span><span class="o">))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">					<span class="n">BeanDefinitionHolder</span> <span class="n">definitionHolder</span> <span class="o">=</span> <span class="k">new</span> <span class="n">BeanDefinitionHolder</span><span class="o">(</span><span class="n">candidate</span><span class="o">,</span> <span class="n">beanName</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">					<span class="n">definitionHolder</span> <span class="o">=</span>
</span></span><span class="line"><span class="cl">							<span class="n">AnnotationConfigUtils</span><span class="o">.</span><span class="na">applyScopedProxyMode</span><span class="o">(</span><span class="n">scopeMetadata</span><span class="o">,</span> <span class="n">definitionHolder</span><span class="o">,</span> <span class="k">this</span><span class="o">.</span><span class="na">registry</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">					<span class="n">beanDefinitions</span><span class="o">.</span><span class="na">add</span><span class="o">(</span><span class="n">definitionHolder</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">					<span class="c1">// 注册BeanDefinition
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>					<span class="n">registerBeanDefinition</span><span class="o">(</span><span class="n">definitionHolder</span><span class="o">,</span> <span class="k">this</span><span class="o">.</span><span class="na">registry</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="o">}</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="k">return</span> <span class="n">beanDefinitions</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><h3 id="25-findcandidatecomponents原理解析">2.5 findCandidateComponents原理解析</h3>
<p>最终会执行到scanCandidateComponents()方法。从下面源码中可以看到，实际上就是根据<code>&lt;context:component-scan/&gt;</code>标签配置的<code>base-package</code>来扫描对应路径下的文件输入流，读取类文件信息。进而拿到Class对象，封装成BeanDefinition对象。然后向上返回，直到注册到BeanDefinitionRegistry中。</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">ComponentScanBeanDefinitionParser</span> <span class="kd">implements</span> <span class="n">BeanDefinitionParser</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">	<span class="kd">private</span> <span class="n">Set</span><span class="o">&lt;</span><span class="n">BeanDefinition</span><span class="o">&gt;</span> <span class="nf">scanCandidateComponents</span><span class="o">(</span><span class="n">String</span> <span class="n">basePackage</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="n">Set</span><span class="o">&lt;</span><span class="n">BeanDefinition</span><span class="o">&gt;</span> <span class="n">candidates</span> <span class="o">=</span> <span class="k">new</span> <span class="n">LinkedHashSet</span><span class="o">&lt;&gt;();</span>
</span></span><span class="line"><span class="cl">		<span class="k">try</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="c1">//根据路径扫描
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="n">String</span> <span class="n">packageSearchPath</span> <span class="o">=</span> <span class="n">ResourcePatternResolver</span><span class="o">.</span><span class="na">CLASSPATH_ALL_URL_PREFIX</span> <span class="o">+</span>
</span></span><span class="line"><span class="cl">					<span class="n">resolveBasePackage</span><span class="o">(</span><span class="n">basePackage</span><span class="o">)</span> <span class="o">+</span> <span class="sc">&#39;/&#39;</span> <span class="o">+</span> <span class="k">this</span><span class="o">.</span><span class="na">resourcePattern</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">			<span class="c1">// 获取指定包下匹配到的所有的资源对象。里面封装了InputStream，用来读取类文件。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="n">Resource</span><span class="o">[]</span> <span class="n">resources</span> <span class="o">=</span> <span class="n">getResourcePatternResolver</span><span class="o">().</span><span class="na">getResources</span><span class="o">(</span><span class="n">packageSearchPath</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">			<span class="kt">boolean</span> <span class="n">traceEnabled</span> <span class="o">=</span> <span class="n">logger</span><span class="o">.</span><span class="na">isTraceEnabled</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">			<span class="kt">boolean</span> <span class="n">debugEnabled</span> <span class="o">=</span> <span class="n">logger</span><span class="o">.</span><span class="na">isDebugEnabled</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">			<span class="k">for</span> <span class="o">(</span><span class="n">Resource</span> <span class="n">resource</span> <span class="o">:</span> <span class="n">resources</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="k">if</span> <span class="o">(</span><span class="n">traceEnabled</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">					<span class="n">logger</span><span class="o">.</span><span class="na">trace</span><span class="o">(</span><span class="s">&#34;Scanning &#34;</span> <span class="o">+</span> <span class="n">resource</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="o">}</span>
</span></span><span class="line"><span class="cl">				<span class="k">if</span> <span class="o">(</span><span class="n">resource</span><span class="o">.</span><span class="na">isReadable</span><span class="o">())</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">					<span class="k">try</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">						<span class="c1">// 封装成ScannedGenericBeanDefinition，这里封装了包下所有的类信息
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>						<span class="n">MetadataReader</span> <span class="n">metadataReader</span> <span class="o">=</span> <span class="n">getMetadataReaderFactory</span><span class="o">().</span><span class="na">getMetadataReader</span><span class="o">(</span><span class="n">resource</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">						<span class="k">if</span> <span class="o">(</span><span class="n">isCandidateComponent</span><span class="o">(</span><span class="n">metadataReader</span><span class="o">))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">							<span class="c1">// 创建BeanDefinition对象，将
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>							<span class="n">ScannedGenericBeanDefinition</span> <span class="n">sbd</span> <span class="o">=</span> <span class="k">new</span> <span class="n">ScannedGenericBeanDefinition</span><span class="o">(</span><span class="n">metadataReader</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">							<span class="n">sbd</span><span class="o">.</span><span class="na">setResource</span><span class="o">(</span><span class="n">resource</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">							<span class="n">sbd</span><span class="o">.</span><span class="na">setSource</span><span class="o">(</span><span class="n">resource</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">							<span class="c1">// 判断是否是候选组件，如果是，就添加BeanDefinition对象
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>							<span class="k">if</span> <span class="o">(</span><span class="n">isCandidateComponent</span><span class="o">(</span><span class="n">sbd</span><span class="o">))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">								<span class="k">if</span> <span class="o">(</span><span class="n">debugEnabled</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">									<span class="n">logger</span><span class="o">.</span><span class="na">debug</span><span class="o">(</span><span class="s">&#34;Identified candidate component class: &#34;</span> <span class="o">+</span> <span class="n">resource</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">								<span class="o">}</span>
</span></span><span class="line"><span class="cl">								<span class="n">candidates</span><span class="o">.</span><span class="na">add</span><span class="o">(</span><span class="n">sbd</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">							<span class="o">}</span>
</span></span><span class="line"><span class="cl">							<span class="k">else</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">								<span class="k">if</span> <span class="o">(</span><span class="n">debugEnabled</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">									<span class="n">logger</span><span class="o">.</span><span class="na">debug</span><span class="o">(</span><span class="s">&#34;Ignored because not a concrete top-level class: &#34;</span> <span class="o">+</span> <span class="n">resource</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">								<span class="o">}</span>
</span></span><span class="line"><span class="cl">							<span class="o">}</span>
</span></span><span class="line"><span class="cl">						<span class="o">}</span>
</span></span><span class="line"><span class="cl">						<span class="k">else</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">							<span class="k">if</span> <span class="o">(</span><span class="n">traceEnabled</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">								<span class="n">logger</span><span class="o">.</span><span class="na">trace</span><span class="o">(</span><span class="s">&#34;Ignored because not matching any filter: &#34;</span> <span class="o">+</span> <span class="n">resource</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">							<span class="o">}</span>
</span></span><span class="line"><span class="cl">						<span class="o">}</span>
</span></span><span class="line"><span class="cl">					<span class="o">}</span>
</span></span><span class="line"><span class="cl">					<span class="k">catch</span> <span class="o">(</span><span class="n">Throwable</span> <span class="n">ex</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">						<span class="k">throw</span> <span class="k">new</span> <span class="n">BeanDefinitionStoreException</span><span class="o">(</span>
</span></span><span class="line"><span class="cl">								<span class="s">&#34;Failed to read candidate component class: &#34;</span> <span class="o">+</span> <span class="n">resource</span><span class="o">,</span> <span class="n">ex</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">					<span class="o">}</span>
</span></span><span class="line"><span class="cl">				<span class="o">}</span>
</span></span><span class="line"><span class="cl">				<span class="k">else</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">					<span class="k">if</span> <span class="o">(</span><span class="n">traceEnabled</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">						<span class="n">logger</span><span class="o">.</span><span class="na">trace</span><span class="o">(</span><span class="s">&#34;Ignored because not readable: &#34;</span> <span class="o">+</span> <span class="n">resource</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">					<span class="o">}</span>
</span></span><span class="line"><span class="cl">				<span class="o">}</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="k">catch</span> <span class="o">(</span><span class="n">IOException</span> <span class="n">ex</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="k">throw</span> <span class="k">new</span> <span class="n">BeanDefinitionStoreException</span><span class="o">(</span><span class="s">&#34;I/O failure during classpath scanning&#34;</span><span class="o">,</span> <span class="n">ex</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="k">return</span> <span class="n">candidates</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><h2 id="3-aspectjautoproxybeandefinitionparser">3 AspectJAutoProxyBeanDefinitionParser</h2>
<hr>
<p>AspectJAutoProxyBeanDefinitionParser是对aop标签的<a href="aop:aspectj-autoproxy/" rel="">aop:aspectj-autoproxy/</a>的支持<br>
源码：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">class</span> <span class="nc">AspectJAutoProxyBeanDefinitionParser</span> <span class="kd">implements</span> <span class="n">BeanDefinitionParser</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="nd">@Override</span>
</span></span><span class="line"><span class="cl">	<span class="nd">@Nullable</span>
</span></span><span class="line"><span class="cl">	<span class="kd">public</span> <span class="n">BeanDefinition</span> <span class="nf">parse</span><span class="o">(</span><span class="n">Element</span> <span class="n">element</span><span class="o">,</span> <span class="n">ParserContext</span> <span class="n">parserContext</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 对aspectj-autoproxy属性的支持
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="n">AopNamespaceUtils</span><span class="o">.</span><span class="na">registerAspectJAnnotationAutoProxyCreatorIfNecessary</span><span class="o">(</span><span class="n">parserContext</span><span class="o">,</span> <span class="n">element</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 添加IncludePatterns
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="n">extendBeanDefinition</span><span class="o">(</span><span class="n">element</span><span class="o">,</span> <span class="n">parserContext</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="k">return</span> <span class="kc">null</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>会走到这里：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">abstract</span> <span class="kd">class</span> <span class="nc">AopConfigUtils</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">	<span class="nd">@Nullable</span>
</span></span><span class="line"><span class="cl">	<span class="kd">public</span> <span class="kd">static</span> <span class="n">BeanDefinition</span> <span class="nf">registerAspectJAnnotationAutoProxyCreatorIfNecessary</span><span class="o">(</span>
</span></span><span class="line"><span class="cl">			<span class="n">BeanDefinitionRegistry</span> <span class="n">registry</span><span class="o">,</span> <span class="nd">@Nullable</span> <span class="n">Object</span> <span class="n">source</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 注入此类 AnnotationAwareAspectJAutoProxyCreator，本质还是一个BeanPostProcessor,
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="c1">// 实现了BeanPostProcessor的子接口：SmartInstantiationAwareBeanPostProcessor
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="k">return</span> <span class="n">registerOrEscalateApcAsRequired</span><span class="o">(</span><span class="n">AnnotationAwareAspectJAutoProxyCreator</span><span class="o">.</span><span class="na">class</span><span class="o">,</span> <span class="n">registry</span><span class="o">,</span> <span class="n">source</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>AopConfigUtils.registerAspectJAnnotationAutoProxyCreatorIfNecessary()方法中，注册了AnnotationAwareAspectJAutoProxyCreator的支持，<code>这个类会在AOP知识点中详细阐述</code>。</p>
<h2 id="4-annotationconfigbeandefinitionparser">4 AnnotationConfigBeanDefinitionParser</h2>
<p>在其源码 parse() 中有这么一段代码。</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">AnnotationConfigBeanDefinitionParser</span> <span class="kd">implements</span> <span class="n">BeanDefinitionParser</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">	<span class="kd">public</span> <span class="n">BeanDefinition</span> <span class="nf">parse</span><span class="o">(</span><span class="n">Element</span> <span class="n">element</span><span class="o">,</span> <span class="n">ParserContext</span> <span class="n">parserContext</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="n">Object</span> <span class="n">source</span> <span class="o">=</span> <span class="n">parserContext</span><span class="o">.</span><span class="na">extractSource</span><span class="o">(</span><span class="n">element</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// TODO 重点看下，逻辑相对简单，注册一些内置注解解析支持
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="n">Set</span><span class="o">&lt;</span><span class="n">BeanDefinitionHolder</span><span class="o">&gt;</span> <span class="n">processorDefinitions</span> <span class="o">=</span>
</span></span><span class="line"><span class="cl">				<span class="n">AnnotationConfigUtils</span><span class="o">.</span><span class="na">registerAnnotationConfigProcessors</span><span class="o">(</span><span class="n">parserContext</span><span class="o">.</span><span class="na">getRegistry</span><span class="o">(),</span> <span class="n">source</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">        <span class="c1">// 省略...
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="k">return</span> <span class="kc">null</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>进入 registerAnnotationConfigProcessors()：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">abstract</span> <span class="kd">class</span> <span class="nc">AnnotationConfigUtils</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">    <span class="kd">public</span> <span class="kd">static</span> <span class="n">Set</span><span class="o">&lt;</span><span class="n">BeanDefinitionHolder</span><span class="o">&gt;</span> <span class="nf">registerAnnotationConfigProcessors</span><span class="o">(</span>
</span></span><span class="line"><span class="cl">			<span class="n">BeanDefinitionRegistry</span> <span class="n">registry</span><span class="o">,</span> <span class="nd">@Nullable</span> <span class="n">Object</span> <span class="n">source</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// ApplicationContext是实现了BeanDefinitionRegistry的，这里将ApplicationContext进行强转。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="n">DefaultListableBeanFactory</span> <span class="n">beanFactory</span> <span class="o">=</span> <span class="n">unwrapDefaultListableBeanFactory</span><span class="o">(</span><span class="n">registry</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 省略...
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="n">Set</span><span class="o">&lt;</span><span class="n">BeanDefinitionHolder</span><span class="o">&gt;</span> <span class="n">beanDefs</span> <span class="o">=</span> <span class="k">new</span> <span class="n">LinkedHashSet</span><span class="o">&lt;&gt;(</span><span class="n">8</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">		<span class="c1">// ConfigurationClassPostProcessor注册，支持注解@Configuration
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="k">if</span> <span class="o">(!</span><span class="n">registry</span><span class="o">.</span><span class="na">containsBeanDefinition</span><span class="o">(</span><span class="n">CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME</span><span class="o">))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="c1">// 这里注入了一个BeanFactoryPostProcessor
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="n">RootBeanDefinition</span> <span class="n">def</span> <span class="o">=</span> <span class="k">new</span> <span class="n">RootBeanDefinition</span><span class="o">(</span><span class="n">ConfigurationClassPostProcessor</span><span class="o">.</span><span class="na">class</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">			<span class="n">def</span><span class="o">.</span><span class="na">setSource</span><span class="o">(</span><span class="n">source</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">			<span class="n">beanDefs</span><span class="o">.</span><span class="na">add</span><span class="o">(</span><span class="n">registerPostProcessor</span><span class="o">(</span><span class="n">registry</span><span class="o">,</span> <span class="n">def</span><span class="o">,</span> <span class="n">CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME</span><span class="o">));</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// AutowiredAnnotationBeanPostProcessor注册，支持@Autowired
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="k">if</span> <span class="o">(!</span><span class="n">registry</span><span class="o">.</span><span class="na">containsBeanDefinition</span><span class="o">(</span><span class="n">AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME</span><span class="o">))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="n">RootBeanDefinition</span> <span class="n">def</span> <span class="o">=</span> <span class="k">new</span> <span class="n">RootBeanDefinition</span><span class="o">(</span><span class="n">AutowiredAnnotationBeanPostProcessor</span><span class="o">.</span><span class="na">class</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">			<span class="n">def</span><span class="o">.</span><span class="na">setSource</span><span class="o">(</span><span class="n">source</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">			<span class="n">beanDefs</span><span class="o">.</span><span class="na">add</span><span class="o">(</span><span class="n">registerPostProcessor</span><span class="o">(</span><span class="n">registry</span><span class="o">,</span> <span class="n">def</span><span class="o">,</span> <span class="n">AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME</span><span class="o">));</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 省略...
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="k">return</span> <span class="n">beanDefs</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>可以看到，这里注册了 ConfigurationClassPostProcessor 和 AutowiredAnnotationBeanPostProcessor。</p>
<p>这些都是内置的 BeanDefinitionPostProcessor 实现类，对应注解都是常用的，有必要看一下。</p>
<h2 id="5-总结">5 总结</h2>
<hr>
<p>spring对XML的解析，就是通过NameSpaceHandler中注册的BeanDefinitionParser进行处理的。通过SPI的方式，很容易对标签解析功能进行扩展。
<div class="details admonition tip open">
        <div class="details-summary admonition-title">
            <i class="icon fas fa-lightbulb fa-fw"></i>技巧<i class="details-icon fas fa-angle-right fa-fw"></i>
        </div>
        <div class="details-content">
            <div class="admonition-content"><p>其他的解析类，方法都是一样的。</p>
<ol>
<li>首先根据标签名称找到NamespaceUri，根据SPI加载方式，到对应模块META-INF/spring.handlers文件中查找对应的NamespaceHandler实现类；</li>
<li>然后在实现类中的init方法中，找到标签属性对应的BeanDefinitionParser实现类；</li>
<li>最后，进入实现类的parse方法，读源码即可。结合断点调试，很容易读懂。</li>
</ol>
</div>
        </div>
    </div></p>
<p>万事开头难，spring源码也一样。刚开始确实挺难理解的，理清了脉络后，再读起来就相对简单很多。</p></div>

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